It has been proposed to increase efficiency in the distribution of computer software by distributing many software programs on a single CD-ROM instead of distributing each program on a separate floppy disk or set of floppy disks. In this proposed distribution system, a customer who has the CD-ROM (hereinafter sometimes referred to as "the disk") in his possession and desires to obtain access to one of the programs on the disk purchases an access code which may be used to gain access to the desired program.
In order to carry out this software distribution system, it is desirable to provide a serial number or identification number on the disk in machine-readable form so that access codes can, through encryption, be limited to use with only one disk serial number, thereby preventing unauthorized use of the access code on more than one disk. However, the most efficient manner of producing CD-ROMs is by molding each disk from a master, which results in each disk containing identical recorded information. In other words, if a conventional mastering process is used to record a "serial" number on the disk, each disk formed from a given master will have the same "serial" number. It has been proposed to use approximately 20 different masters to produce compact disks which contain identical software program information, with each master respectively used to produce disks having an identification number that is different from the identification numbers of disks produced using different masters. However, this approach suffers from two drawbacks: First, the cost of mastering is significantly increased, and secondly, the number of different disk identification numbers is the same as the number of different masters, i.e. about 20, which makes it relatively easy for unscrupulous persons to locate disks having the same identification number and then to use a single access code to "unlock" the same program on all of the disks which have the same identification code.
It is also possible to use disk manufacturing processes without molding from a master, with a unique serial number being recorded on each disk at the same time the program software is recorded, for example by magneto-optical recording, but such processes are substantially more expensive than molding CD-ROMs from a master.
Another constraint on provision of serial numbers on CD-ROMs is the need for the serial number to be readable using conventional hardware such as generally available CD-ROM drives interfaced to personal computers.